Electromotive force and impedance studies of cellulose acetate membranes: Evidence for two binding sites for divalent cations and for an alveolar structure of the skin layer

摘要: Abstract The electromotive force (EMF) has been measured for a great number of concentration cells the type: Ag | AgCl ⋎ ⪢variable⪡ solution Cellulose Acetate Membrane ⪢fixed⪡ Ag. solutions were aqueous mixed electrolytes at atmospheric pressure and mostly 25°C (in some few cases 35°C ). ions considered cations H + , Li Na K Mg ++ Ca Ba anions Cl − F (Cl was always present). same in each series experiments, but may be varied from one to next. In solution, least electrolyte during EMF measurements. variable over almost 4 decades (from 10 −4 M 0.6−1.0 M). 2.5-Cellulose (CA) membranes dense cast by ourselves. A asymmetic membranes. skin layer asymmetric is assumed have properties similar measurements interpreted means Donnan-Nernst-Planck (Toorell-Meyer-Sievers) model, which functions quite well due low fixed charge membrane. membrane diffusion potential calculated Henderson method solving transcendental equations according Planck, Pleijel Schlogl. There no difference between potentials two methods, ion profiles actual rates electrodiffusion found latter method. Earlier results are recapitulated, especially evidence an alveolar structure interpreting capacitance increase with salt - impedance light combined Trukhan-Bruggemann theory. Alveoles or seem mean radius corresponding ca. 70 A. dielectric constant alveoles 30 contrast 16 ⪢lamellar phase⪡ inbetween alveoles. phase also supported simple calculation Nernst distribution mono- divalent external water solution. Corrections activity coefficients only seems important above 0.5 M. Onsager-Samaras repulsion lamellar wall significance concentrations. Measured CA-membranes agree roughly values. We focus on new binding glucuronic acid groups CA-chains, temporarily transform weak cationic exchange anionic washed out, rate dissociation very low. relaxations, slower being order weeks, faster days. followed different concentrations NaCl. slow relaxation connected Coulomb interaction COO ions, whereas fast probably reflecting physical dipole-ion bonds.